Known in the art is a process for producing liquid combined fertilizers (LCF) by way of neutralization in a jet-type reactor of extraction phosphoric acid containing 60-72% P.sub.2 O.sub.5 (10-35% of P.sub.2 O.sub.5 being present in the polyform) by means of gaseous ammonia supplied in an amount close to that in the final product, followed by mixing and cooling of the reaction products with water in another apparatus (cf. U.S. Pat. No. 3,950,495 published Apr. 13, 1976). The thus-obtained products are then mixed in a turbulent reactor with a portion of the final product which has been preliminarily cooled in external coolers-heat-exchangers and post-neutralized in a special apparatus.
The process disadvantage resides in the multi-stage character of the production of LCF which results in an increased number of items of the process equipment and complicates the plant operation; it is also necessary to provide for a forced external recycle of the LCF with the use of pumping means; the disadvantage of the process also resides in the difficulty of obtaining LCF with the content of polyform P.sub.2 O.sub.5 of above 40% by weight from extraction phosphoric acid containing P.sub.2 O.sub.5 polyform in an amount below 10% by weight.
The closest prior art process is a process for producing liquid combined fertilizers (LCF) (cf. British Pat. No. 1,379,796 Cl. C IA C3 A D 37), wherein extraction phosphoric acid pre-evaporated and heated to a temperature of 112.degree.-224.degree. C. consisting of ortho-polyforms or an acid produced by intermixing ortho-phosphoric and polyphosphoric acids with a concentration of P.sub.2 O.sub.5 of 62-70% is fed simultaneously with gaseous ammonia into an isothermal reactor maintained under a pressure of 0.5 to 20 atm and at a temperature of 278.degree. to 427.degree. C. due to heat of neutralization. Ammonia is fed in an amount necessary for the production of a partly neutralized melt of ammonium polyphosphate. The reaction products at a temperature of essentially 354.degree.-389.degree. C. are delivered to a mixer, whereinto ammonia and water or ammonia water are also supplied in an amount equal to the content thereof in the final product. Atmospheric pressure and temperature of from 42.degree. to 118.degree. C. are maintained in the mixer due to the recycling of the final product preliminarily cooled in external cooling heat-exchangers. The gases and non-reacted ammonia are passed through packed absorbers, wherein ammonia is trapped by means of water or an aqueous solution of the LCF. The final LCF product has a content of nitrogen of 10 to 13%, a content of P.sub.2 O.sub.5 of 33-37% by weight, wherein the amount of polyforms ranges from 65 to 80% of the total content of P.sub.2 O.sub.5.
The process has the following disadvantages: the removal of the neutralization heat is effected by recycling the major portion of the final product and cooling thereof in external cooling heat-exchangers. Due to a small temperature differential in the heat-exchangers and low coefficient of heat transfer due to a high viscosity of LCF, great surface areas of the heat exchange and powerful pumps are required. Furthermore, a large volume of the apparatus for mixing the reaction products of neutralization with water and the final recycled cooled product leads to local overheatings of the solution, this causing an increased hydrolysis and losses of ammonia which should be trapped in special apparatus-absorbers. The separation of the ammonia stream to the jet-type reactor (and to the post-neutralizer-mixing apparatus and the stream of the LCF to recycling and output of the final product complicate monitoring of the process and obtaining a stable quality of the LCF.
The above disadvantages do not allow the production of LCF with a content of polyforms of above 50% from extraction phosphoric acid with a concentration of below 62% based on P.sub.2 O.sub.5, or from acids with a content of polyforms therein below 30%.